Purpose:
Amblyopia is a common developmental visual disorder characterized by interocular acuity differences and associated with low functional vision. It is typically treated by refractive correction followed by either patching or pharmacological blurring of the better seeing eye. Such treatments have imperfect efficacy (success rates: acuity, 20% to 90%; stereoacuity, <50%) and poor compliance (44-57%), and they show a high risk of recurrence after cessation (~30% at one year follow-up). We propose a treatment for amblyopia that addresses these limitations.

Methods:
We tested a novel “binocular balanced viewing” (BBV) therapy on 8 children (7-12yrs) with anisometropic unilateral amblyopia (2 or more logMAR lines interocular difference in best corrected visual acuity after full refractive adaptation). Children spent ~50min/day watching movies at home while wearing goggle-mounted 3D-shutter glasses. We "balanced" the visibility of the movie across eyes by applying sufficient Gaussian blur to the image presented to the unaffected eye to reduce its crowded-acuity to the level of the affected eye. Although 2D movies were used, image-disparity was modulated slowly over time to provide stimulation at a range of depth-planes. During movie playback children also made a series of perceptual judgements (treatment's active component, involving dichoptic video-game characters) and their performance yielded a day-to-day index of compliance and inter-ocular suppression.

Results:
After ~60 hours of treatment (achieved in ~8 weeks) we observed substantial improvement (average 3.20 logMAR lines) in acuity in the affected eye and near-normal stereo vision (Frisby test: 85 seconds of arc or better; mean improvement of 180 sec arc) in all but one participant. One child did not attend the post-treatment review and was excluded from analysis. At our daily measurements, compliance was high (average 50min/day; mean daily compliance 70%) and inter-ocular suppression remained largely unaffected by treatment, even in cases where substantial gains in acuity were achieved.

Conclusions:
These exploratory findings are encouraging and suggest that BBV therapy may have wider applicability in the treatment of amblyopia. It leads to rapid and substantial functional gains compared to standard interventions while being, unlike occlusion therapy, popular with patients and parents (maximizing compliance and outcome).